Since 1976, 15 national metrology institutes (NMIs) and two other laboratories have submitted 34 samples of known activity of ¹³⁷Cs to the International Reference System (SIR) for activity comparison at the Bureau International des Poids et Mesures. The activities ranged from about 550 kBq to 67 MBq. The degrees of equivalence between each equivalent activity measured in the SIR and the key comparison reference value (KCRV) have been calculated and the results are given in the form of a matrix for eleven NMIs and the BIPM. A graphical presentation is also given.

Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.

The final report has been peer-reviewed and approved for publication by Section II of the Consultative Committee for Ionizing Radiation (CCRI(II)), comparison identifier BIPM.RI(II)-K1.Cs-137, according to the provisions of the Mutual Recognition Arrangement (MRA). The results of a CCRI international comparison, identifier CCRI(II)-K2.Cs-137 held in 1982 that have been approved for provisional equivalence for this radionuclide, have been linked to the SIR results. This has enabled three NMIs to update their results and a further three NMIs and one international laboratory, the IRMM, to be linked to the SIR.